A two-way satellite communication system of VSAT (very small aperture terminal) type consists of a central hub and a large number of terminals. These terminals are typically spread over a large area—this area can be as large as a continent. In such a configuration, each one of the remote (VSAT) terminals is in two-way communication with the hub through a satellite. The architecture of such a VSAT based system is disclosed in U.S. Pat. Nos. 6,233,429 (Soffer et al.), for a VSAT Satellite Communication System, and 5,053,782 (Levinberg et al.), for a Commercial Satellite Communication System, which are assigned to Gilat, the Assignee of the present invention, and which are incorporated herein by reference.
In the satellite communication systems described in the Soffer et al. and Levinberg et al. patents, the data service transmitted outbound from the central hub to each one of the remote terminals can be one of two different types:                (a) a Unicast connection, in which data is sent from the hub to each VSAT terminal separately, as part of a private session between the hub and each specific terminal, and        (b) a Multicast connection, in which data is sent (broadcasted) from the hub to groups of VSAT terminals, each group consists of any number of VSAT terminals, and all the VSAT terminals in a group receive the same Multicast information.        
Satellite bandwidth is a major resource that is used by the VSAT network described in the Soffer et al. and Levinberg et al. systems. Normally such a network has a pre-assigned bandwidth in the satellite for both of the transmit directions, i.e., inbound—from the VSAT terminals to the hub, and outbound—from the hub to the VSAT terminals) and for both types of services (Unicast and Multicast). Because the satellite bandwidth resources are limited, bandwidth management is highly important for large networks. Satellite-based communications systems consist of several “channels”, each of which covers a certain frequency band. Normally, but not necessarily, each channel is attributed to and works through a transponder in the satellite. The overall bandwidth capacity of the satellite is determined by the frequency band of each channel multiplied by the number of available channels or transponders. In a typical large network, the VSAT terminals are divided between transponders, such that each transponder serves a group of VSAT terminals.
There is no relation between the partitioning of VSAT terminals into channels, and the definition of VSAT terminal groups for Multicast broadcasting. The VSAT terminals that are tuned to different channels may or may not be assigned to the same Multicast group for a specific broadcast. In order to enable each VSAT terminal in the system to receive the Multicast transmissions, regardless of the channel it is tuned to, the same Multicast information has to be transmitted on each channel, in addition to the Unicast information. FIG. 2 illustrates this schema.
As shown in FIG. 1, the system 5 includes a satellite 18, multiple remote sites 10, each having a very small aperture antenna 14, and a hub site 20. The remote sites 10 include VSAT terminals VSAT 1 through VSAT m, as shown in FIG. 2. Each VSAT terminal has a single receiver. In the illustrated example shown in FIG. 2, the satellite 18 communicates with VSAT terminals via Channel 1 through Channel n. Each VSAT terminal 10 receives both Unicast and Multicast data via its assigned channel. As a result, in order to communicate Multicast data to the VSAT terminals 10, the satellite 18 must broadcast the data over all of the channels, Channel 1 through Channel n. Such broadcasting makes very inefficient use of the available bandwidth.
This duplication of Multicast information over all the channels 1 through n in the satellite 18 imposes a significant inefficiency of bandwidth utilization. Since the bandwidth in a satellite communication network 5 is an expensive resource, this inefficiency has a major cost impact on the whole VSAT network and the price, which consumers of such a product need to pay.
Thus, there exists a need in the art for a method, device, and system, which makes more efficient use of the available bandwidth for Unicast and Multicast information transmission.